Electromotors which convert electrical into mechanical energy by means of the electromagnetic principle have the disadvantage that there is electrical and mechanical inertia at the rotors.
Actuatorelectric drives in which either an inverted piezoelectric effect on polarized crystals, magnetostrictive effects or the like are used, lead one to expect low inertias. In such cases it is necessary to arrange actuators in series, in order to form a longer stroke from the oscillating travel of the actuators when alternating voltage is applied. Various suggestions have been made in this connection.
One of these suggestions hydraulically converts the slight stroke of an actuator into a longer stroke according to the principle of variable piston surfaces. The disadvantage of this suggestion, however, is that the overall size of the structure is excessive and the hydraulic unit easily begins to leak.
In so-called ultrasound motors, e.g. the rotary control drive described in patent publication EP 0 112 454 B1, the main problem is the mechanical wear at the contact point between piezoelectric crystal actuator and rotor which, in most cases, restricts its life or even makes operation impossible, particularly in small structures.
Low-wear surface coatings and soft intermediate layers were suggested which soften the hard impact of the actuator end on the rotor. However, the problems are not adequately solved with these structures.
The so-called inchworm motor also has disadvantages of this type. Two piezoelectric crystal sleeves are wedged in a round guide shaft, whereby a longitudinal piezoelectric crystal located between them ensures that a corresponding unclamped sleeve is advanced within the shaft. Its operation is quite heavily dependent on the wear between the piezoelectric sleeve and shaft.
It was also suggested that piezoelectric crystals be allowed to radially or angularly strike against a rotor in an oscillating manner. However tangential and radial oscillation amplitudes cannot be cleanly separated even at the control side and, therefore, additional wear results.
The very slight stroke of the actuators is easily offset by play and wear in the mechanical arrangement and the device thus made ineffective. Otherwise, the structure must be made appropriately rigid and precise and is thus expensive.
These problems occur in linear motors, as well as in rotary motors and piezoelectric crystals and also when using other actuators.
An object of the invention is to improve an actuatorelectric motor and its electronic control in such a way that these disadvantages are eliminated.